JSON Formatter

Formatting and validation are the same operation

A formatter has to parse before it can indent, so every formatter is also a validator. What separates a useful one is the quality of the error message when parsing fails. This tool reports the line and column where the parse broke and what it expected, rather than the browser's default message, which frequently points at the closing brace instead of the actual mistake several lines earlier.

The errors you will actually hit

Trailing commas after the last element are the most common, because JavaScript object literals allow them and JSON does not. Single quotes around strings are second: JSON requires double quotes for both keys and values. Unquoted keys are third, again a JavaScript habit. Then there are unescaped control characters inside strings, usually a literal newline pasted out of a log file, and NaN or Infinity, which JavaScript produces but JSON has no representation for.

A subtler one is a byte order mark on a file exported from a Windows editor. The JSON looks perfect and still fails, because there is an invisible U+FEFF before the opening brace. This tool strips a leading BOM and tells you it did.

Large numbers lose precision

JSON has one numeric type and JavaScript parses it as a double. Any integer beyond 2^53-1 silently loses precision, which bites when a payload carries 64-bit database identifiers or snowflake IDs. If your data contains large integer IDs they should be transmitted as strings. The formatter flags integers past the safe range rather than quietly rounding them.

Nothing is uploaded

Parsing happens in your browser using the native JSON parser. No request is made and the payload never leaves the machine. That matters because the JSON people most often need to format is an API response containing tokens, customer records or internal identifiers, and pasting that into a server-side formatter is a data disclosure.

Minify as well as beautify

The same parse supports the reverse operation: stripping insignificant whitespace for transport. For a typical API response that removes 15 to 30 percent of the bytes before compression, though gzip closes most of the gap, so minified JSON matters far more for payload size limits than for bandwidth.

Related tools

• JSON Validator — Validate JSON syntax with precise line and column errors, and check documents against a JSON Schema. Runs locally in your browser, nothing uploaded.
• Regex Tester — Test regular expressions against sample text with live match highlighting, capture groups and flag control. Runs entirely in your browser.
• HTML Minifier — Minify HTML by removing comments and redundant whitespace, without breaking inline elements or pre blocks. Runs entirely in your browser.
• CSS Minifier — Minify CSS by stripping comments and whitespace safely. Runs in your browser with no upload, and reports the byte saving before and after gzip.